I agree, your explanation with the surface configuration does better
explain what really happens.

Thank you

Urs

> I would expect the single foil rolled up with a dielectric to
>give different results from the uninsulated foil, because the
>dielectric increases the separation between layers and reduces the
>electric field between layers. I wonder too if some charge will be
>trapped in the innermost layer.
> Rolled foil capacitors such as electrolytics actually hold more
>charge than 2 parallel plates of the same size because each foil is
>flanked on both sides by the opposite polarity plate, allowing it to
>store charge on both sides.
> It seems to me it would be more accurate to explain the example
>of the conductive umbrella as charge being repelled off the umbrella
>(on to the electroscope) as the conductive surfaces come together.
>There is no change in surface area, just in surface configuration...
>
>
>Jerry D
>
>
>At 2/17/2011 09:19 PM, you wrote:
>>Bill,
>>
>>It's the last paragraph of the article that has this error. Here's
>>the citation from December:
>>Tin foil capacitor
>>
>>And if it's not bad form to quote the article here:
>>...... It might be possible to make another tube that has the foil
>>sandwiched between sheets of plastic or paper and then roll up the
>>foil. The plastic should insulate the foil layers when it is rolled
>>up, and therefore there should be no difference in elec- troscope
>>separation when the foil sandwich is unrolled and rolled.
>>......
>>
>>Paul
>
>
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>
> Jerry DiMarco
> Manager of Lecture Demonstrations and Instructional Labs
> Montana State Univ., Physics Dept.
> Bozeman, MT
>
>Our Motto: "A demo a day helps learning to stay"